mm/hmm: remove unused code and tidy comments

Delete several functions that are never called, fix some desync between
comments and structure content, toss the now out of date top of file
header, and move one function only used by hmm.c into hmm.c

Link: https://lore.kernel.org/r/20200327200021.29372-4-jgg@ziepe.ca
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

1 files changed, 17 insertions, 7 deletions

diff --git a/mm/hmm.c b/mm/hmm.c
index d208ddd35106..136de474221d 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -38,6 +38,18 @@ enum {
 	HMM_NEED_ALL_BITS = HMM_NEED_FAULT | HMM_NEED_WRITE_FAULT,
 };
 
+/*
+ * hmm_device_entry_from_pfn() - create a valid device entry value from pfn
+ * @range: range use to encode HMM pfn value
+ * @pfn: pfn value for which to create the device entry
+ * Return: valid device entry for the pfn
+ */
+static uint64_t hmm_device_entry_from_pfn(const struct hmm_range *range,
+					  unsigned long pfn)
+{
+	return (pfn << range->pfn_shift) | range->flags[HMM_PFN_VALID];
+}
+
 static int hmm_pfns_fill(unsigned long addr, unsigned long end,
 		struct hmm_range *range, enum hmm_pfn_value_e value)
 {
@@ -544,7 +556,7 @@ static const struct mm_walk_ops hmm_walk_ops = {
 
 /**
  * hmm_range_fault - try to fault some address in a virtual address range
- * @range:	range being faulted
+ * @range:	argument structure
  * @flags:	HMM_FAULT_* flags
  *
  * Return: the number of valid pages in range->pfns[] (from range start
@@ -558,13 +570,11 @@ static const struct mm_walk_ops hmm_walk_ops = {
  *		only).
  * -EBUSY:	The range has been invalidated and the caller needs to wait for
  *		the invalidation to finish.
- * -EFAULT:	Invalid (i.e., either no valid vma or it is illegal to access
- *		that range) number of valid pages in range->pfns[] (from
- *              range start address).
+ * -EFAULT:     A page was requested to be valid and could not be made valid
+ *              ie it has no backing VMA or it is illegal to access
  *
- * This is similar to a regular CPU page fault except that it will not trigger
- * any memory migration if the memory being faulted is not accessible by CPUs
- * and caller does not ask for migration.
+ * This is similar to get_user_pages(), except that it can read the page tables
+ * without mutating them (ie causing faults).
  *
  * On error, for one virtual address in the range, the function will mark the
  * corresponding HMM pfn entry with an error flag.